實驗與理論研究微結構排列對骨頭與仿骨材料力學行為之影響

Abstract

許多天然生物材料展現出兼具高強度與高韌性的優異性能，其中以骨骼材料最具代表性，長期以來受到學術界廣泛關注。透過微觀尺度的觀察可知，骨頭並非均質材料，而是由軟硬材質（膠原纖維與礦物質）交錯堆疊而成的複合結構，其排列方式形似水泥磚牆，本研究將其定義為「軟硬材疊層結構」。針對此類結構，過去學者提出「拉伸－剪切鏈模型」（tension-shear chain model, TSC model），用以描述材料中軟硬相協同承載的機制，其中硬材負責抵抗軸向拉力，而軟材則主要承擔剪力傳遞，使整體結構展現出良好的承載與變形能力。然而，傳統TSC模型僅假設材料具備線彈性，未能考量膠原纖維在實際行為中展現的黏彈特性。 為克服上述侷限，本研究延伸原有模型，提出一套將軟材行為推廣為黏彈性的「黏彈性拉伸－剪切鏈模型」（viscoelastic TSC model, VE TSC model），使其更能真實模擬材料在實際力學環境下的反應。進一步地，考慮到骨質疏鬆症可能改變骨頭的微結構排列與材料性質，本研究設計三點彎曲實驗，針對健康骨頭與骨質疏鬆骨頭進行力學測試，並透過多階段的分析方法，在複雜載重路徑下解析兩者在剛性、黏彈性常數與能量耗散能力等面向的差異，以深入探討疾病狀態對骨骼力學行為的影響。 此外，微結構排列變化亦被視為影響材料行為的關鍵因素，因此本研究進一步設計多種不同排列形式之微結構試體，並透過3D列印技術製作樣本，進行單軸拉伸測試，結合理論模型的分析結果，系統性探討微結構幾何與排列對整體力學性質的影響。綜合理論模型建立、病理實驗驗證與微結構幾何設計，本研究旨在提供一個完整框架，解析軟硬材複合結構於不同條件下的力學行為，期望對生物力學與仿生材料設計領域提供實質貢獻。

Many natural biological materials exhibit exceptional combinations of strength and toughness, among which bone stands out as a representative example. Due to its remarkable mechanical performance, bone has long been a focal point of research. At the microscale, bone is not a homogeneous material but rather a composite composed of alternating soft and hard phases—primarily collagen fibrils and mineral crystals—arranged in a staggered brick-and-mortar-like configuration. In this study, such architecture is referred to as a "soft-stiff layered structure." To analyze the mechanical behavior of this structure, the tension-shear chain (TSC) model was previously proposed, wherein the hard phase primarily resists axial tension while the soft phase transfers shear forces. This cooperative interaction between the two phases accounts for the overall mechanical robustness of the structure. However, the traditional TSC model assumes linear elastic behavior for both phases and therefore fails to capture the viscoelastic characteristics of bone. To address this limitation, the present study extends the TSC framework by incorporating viscoelasticity into the soft phase, resulting in the development of a viscoelastic tension-shear chain model (VE TSC model). This extension allows for a more realistic representation of time-dependent deformation and energy dissipation behavior. In light of the structural degradation commonly observed in osteoporotic bone, which may alter microstructural alignment and mechanical properties, this study conducts three-point bending experiments on both healthy and osteoporotic bones. Using a stage-based analytical approach, the differences in mechanical behavior—such as stiffness, viscoelastic constants, and energy dissipation—under complex loading paths are systematically examined. Furthermore, recognizing that microstructural geometry significantly influences macroscopic properties, various microstructural configurations were designed and fabricated via 3D printing. These samples were subjected to uniaxial tensile tests and analyzed using the proposed model to elucidate the role of geometric arrangement on mechanical performance. By integrating theoretical modeling, experimental validation, and microstructural design, this study aims to establish a comprehensive framework for understanding the mechanics of soft-hard layered composites, with implications for both biomechanics research and biomimetic material development.